Targeted, controlled use of cold material is used in cryosurgery to devitalize biological tissue. In addition, particularly using flexible probes, foreign bodies are extracted from body cavities by freezing them solid on the cryoprobe or on a probe head; these foreign bodies include for example, swallowed and at the same time accidentally inhaled foreign bodies that must be removed from the respiratory tract. Cryosurgery is, however, also suitable for obtaining tissue samples (biopsy). In this case, a specific area of tissue, the tissue sample, freezes onto the probe head and after separation from the surrounding tissue can be made accessible for examination.
There are various possibilities for deep freezing in surgery. One is based on the Joule-Thomson effect: the atoms or molecules of an expanding fluid and in particular of a gas below the inversion temperature work against mutual attraction with the result that the gas loses internal energy. It cools down. Usually CO2 or N2O are used as the expanding fluid or gas—referred to below as cooling fluid or cooling gas.
Cryosurgical instruments of the type just described usually have a probe that can be transported to the tissue to be treated and also gas line devices which penetrate the probes and release the working gas into the inner volume of the probes where it expands and results cooling down the probe. Since these probes are preferably made of thermally conductive material, this ensures elimination of the tissue heat via the probe and therefore a cooling effect.
In cryoprobes where the cooling effect is generated by decompressing compressed gases, there is frequently a requirement for cooling a larger surface evenly or in accordance with a specific temperature profile. For example, a cryoprobe with a 2 mm diameter is supposed to be cooled evenly over a length of 50 mm.
In such cases, according to the prior art, a plurality of nozzles are distributed inside the cryoprobe to achieve reasonably even cooling. The larger the number of cooling nozzles used, the more evenly the resulting temperature is reached over the length selected. With this procedure, the amount of gas required is divided between a plurality of nozzles. Consequently, the individual nozzles are very small in diameter. At the same time, however, production is disproportionately time-consuming. With small nozzles, close tolerances are placed on the geometry to achieve a constant flow behavior. On principle, smaller nozzle cross-sections are also more susceptible to blockages.
It has also turned out that with cryosurgical instruments according to the prior art it is difficult to implement an essentially constant temperature curve or a predetermined temperature curve. Moreover, the construction of the prior art cryoprobes is very time-consuming and cost-intensive.